Species: Potamogeton robbinsii Oakes

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Potamogeton robbinsii Oakes

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TAXONOMY

Family:

Potamogetonaceae

Genus:

Potamogeton

Species Synonyms:

none

Common Names:

Robbins’s pondweed
flat-leaf pondweed
fern pondweed

DISTRIBUTION

Canada:

southwestern British Columbia, central Alberta, north – east-central Saskatchewan, southeastern Manitoba – western Ontario – Quebec – New Brunswick – Nova Scotia

Saskatchewan:

north – east-central Saskatchewan; Cluff Lake - Lac la Ronge – Prince Albert National Park – Porcupine Hills

Ecoregion:

Mid-Boreal Upland, Mid-Boreal Lowland, Churchill River Upland

HABITAT

Saskatchewan:

shallow water of quiet lakes and ponds

Associated Species:

flat-stem pondweed, small pondweed, water milfoil, white water crowfoot, yellow pond lily

RARITY STATUS

Provincial Status According
to Harms (2003):

Endangered

Nature Conservancy Status:

G5 S2

Saskatchewan Species at
Risk Status:

None

COSEWIC Status:

None

Robbin’s pondweed is threatened because it is rare or uncommon in Saskatchewan. It is usually locally numerous within limited areas. No threats are known or anticipated for this species.

SPECIES DESCRIPTION

Height:

to 100 cm

Roots:

roots fibrous; rhizomes present

Stems:

branched, round, stout, without spots, glands absent; overwintering shoots absent

Leaves:

submersed, crowded, 2-ranked, sessile, 2 – 7 cm long, 3 – 4 mm wide, linear to lance-shaped, base rounded and lobed, stiff, air spaces absent, dark green to reddish-green, veins 20 – 60, margin minutely spiny to saw-toothed; stipules fused to the base of the blade and to each other, greenish brown to white, fibrous, shredding at tip

Inflorescence:

spikes uniform, like a string of beads, 7 – 20 mm long, often in branched clusters 3 – 5 cm long, axillary, erect, cylindrical

Flowers:

small, greenish; tepals 4; stamens 4; carpels 4

Fruits:

one-seeded, and fleshy, stalked, brown, ridged, beak erect

POTAMOGETON KEY FOR SPECIES FOUND IN SASKATCHEWAN

1 Stipular sheaths of submersed leaves fused to base of leaf blade; leaf margins cartilaginous	P. robbinsii
1 Stipular sheaths of submersed leaves free from base of leaf blade; leaf margins not cartilaginous	2

2 Submersed leaves oblong to lance-shaped to nearly round	3
2 Submersed leaves ribbon-like or thread-like	9

3 Leaf margins conspicuously saw-toothed and wavy; overwintering stems present	P. crispus
3 Leaf margins entire or wavy; overwintering stems absent	4

4 Submersed leaves clasping; floating leaves absent	5
4 Submersed leaves not clasping, may be stalked; floating leaves present or absent	6

5 Stipules persistent; rhizome with rusty spots	P. praelongus
5 Stipules shredding into fibres; rhizome not obviously spotted	P. richardsonii

6 Floating leaf blade rounded to heart-shaped; stem rusty or black-spotted; submersed leaves arced	P. amplifolius
6 Floating leaf blade wedge-shaped or rounded; stems without spots; submersed leaves not arced	7

7 Submersed leaves stalked	P. nodosus
7 Submersed leaves sessile	8

8 Fruits plump, stalked; submersed leaf blade 7 – 9-veined	P. alpinus
8 Fruits compressed, not stalked; submersed leaf blade 3 – 19-veined	P. gramineus

9 Floating leaves present on at least come plants in a population
9 Floating leaves absent

10 Air spaces in leaf tissue present and prominent; submersed leaves with distinction between blade and stalk; leaves of two types, the floating ones long-stalked and wider than the submersed ones	P. epihydrus
10 Air spaces in leaf tissue absent or not prominent; blade and petiole not well-differentiated on submersed leaves; leaves uniform, no distinction between the floating and submersed leaves	P. natans

11 Nodes without glands	12
11 Nodes glandular	13

12 Leaves 15 – 35-veined, greater than 2 mm wide; stem wing-flattened	P. zosteriformis
12 Leaves 3 – 5-veined, less than 2 mm wide; stem not wing-flattened	P. foliosus ssp. foliosus

13 Stipules fibrous, whitish	14
13 Stipules not fibrous, green, brown or whitish	15

14 Leaf tip tapered to pointed, leaves thin, 5 -7-nerved; inflorescence stalks at most 5 cm long	P. friesii
14 Leaf tip bristle-tipped; leaves firm, 3-nerved; inflorescence stalks to 9 cm long	P. strictifolius

15 Fruits 2.5 – 3.5 mm long	P. obtusifolius
15 Fruits 1.5 – 2 mm long	16

16 Mature fruits widest at the top; inflorescence stalks 1 – 3 per plant; leaf blade with less than 2 rows of air spaces along midrib	P. pusillus ssp. pusillus
16 Mature fruits widest at the middle; inflorescence stalks more than 3 per plant; leaf blade with 1 – 5 rows of air spaces along midrib	P. pusillus ssp. tenuissimus